From: Mel Gorman <mgorman@suse.de>
To: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, frederic@kernel.org, tglx@linutronix.de,
mtosatti@redhat.com, linux-rt-users@vger.kernel.org,
vbabka@suse.cz, cl@linux.com, paulmck@kernel.org,
willy@infradead.org
Subject: Re: [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support
Date: Thu, 10 Mar 2022 16:31:54 +0000 [thread overview]
Message-ID: <20220310163154.GF4363@suse.de> (raw)
In-Reply-To: <fcdaacf58296dfd826bfdbbd5ef3a06b6e05a456.camel@redhat.com>
On Mon, Mar 07, 2022 at 02:57:47PM +0100, Nicolas Saenz Julienne wrote:
> > > Note that this is not the first attempt at fixing this per-cpu page lists:
> > > - The first attempt[1] tried to conditionally change the pagesets locking
> > > scheme based the NOHZ_FULL config. It was deemed hard to maintain as the
> > > NOHZ_FULL code path would be rarely tested. Also, this only solves the issue
> > > for NOHZ_FULL setups, which isn't ideal.
> > > - The second[2] unanimously switched the local_locks to per-cpu spinlocks. The
> > > performance degradation was too big.
> > >
> >
> > For unrelated reasons I looked at using llist to avoid locks entirely. It
> > turns out it's not possible and needs a lock. We know "local_locks to
> > per-cpu spinlocks" took a large penalty so I considered alternatives on
> > how a lock could be used. I found it's possible to both remote drain
> > the lists and avoid the disable/enable of IRQs entirely as long as a
> > preempting IRQ is willing to take the zone lock instead (should be very
> > rare). The IRQ part is a bit hairy though as softirqs are also a problem
> > and preempt-rt needs different rules and the llist has to sort PCP
> > refills which might be a loss in total. However, the remote draining may
> > still be interesting. The full series is at
> > https://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git/ mm-pcpllist-v1r2
>
> I'll have a proper look at it soon.
>
Thanks. I'm still delayed actually finishing the series as most of my
time is dedicated to a separate issue. However, there is at least one
bug in there at patch "mm/page_alloc: Remotely drain per-cpu lists"
that causes a lockup under severe memory pressure. The fix is
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c9a6f2b5548e..11b54f383d04 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3065,10 +3065,8 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
{
- unsigned long flags;
int to_drain, batch;
- pcp_local_lock(&pagesets.lock, flags);
batch = READ_ONCE(pcp->batch);
to_drain = min(pcp->count, batch);
if (to_drain > 0) {
@@ -3076,7 +3074,6 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
free_pcppages_bulk(zone, to_drain, pcp, 0);
spin_unlock(&pcp->lock);
}
- pcp_local_unlock(&pagesets.lock, flags);
}
#endif
@@ -3088,16 +3085,12 @@ static void drain_pages_zone(unsigned int cpu, struct zone *zone)
unsigned long flags;
struct per_cpu_pages *pcp;
- pcp_local_lock(&pagesets.lock, flags);
-
pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
if (pcp->count) {
spin_lock(&pcp->lock);
free_pcppages_bulk(zone, pcp->count, pcp, 0);
spin_unlock(&pcp->lock);
}
-
- pcp_local_unlock(&pagesets.lock, flags);
}
/*
next prev parent reply other threads:[~2022-03-10 16:32 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-08 10:07 [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support Nicolas Saenz Julienne
2022-02-08 10:07 ` [PATCH 1/2] mm/page_alloc: Access lists in 'struct per_cpu_pages' indirectly Nicolas Saenz Julienne
2022-03-03 14:33 ` Marcelo Tosatti
2022-02-08 10:07 ` [PATCH 2/2] mm/page_alloc: Add remote draining support to per-cpu lists Nicolas Saenz Julienne
2022-02-08 15:47 ` Marcelo Tosatti
2022-02-15 8:47 ` Nicolas Saenz Julienne
2022-02-15 17:32 ` Paul E. McKenney
2022-02-09 8:55 ` [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support Xiongfeng Wang
2022-02-09 9:45 ` Nicolas Saenz Julienne
2022-02-09 11:26 ` Xiongfeng Wang
2022-02-09 11:36 ` Nicolas Saenz Julienne
2022-02-10 10:59 ` Xiongfeng Wang
2022-02-10 11:04 ` Nicolas Saenz Julienne
2022-03-03 11:45 ` Mel Gorman
2022-03-07 13:57 ` Nicolas Saenz Julienne
2022-03-10 16:31 ` Mel Gorman [this message]
2022-03-07 20:47 ` Marcelo Tosatti
2022-03-24 18:59 ` Nicolas Saenz Julienne
2022-03-25 10:48 ` Mel Gorman
2022-03-28 13:51 ` Nicolas Saenz Julienne
2022-03-29 9:45 ` Mel Gorman
2022-03-30 11:29 ` Nicolas Saenz Julienne
2022-03-31 15:24 ` Mel Gorman
2022-03-03 13:27 ` Vlastimil Babka
2022-03-03 14:10 ` Nicolas Saenz Julienne
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